2021
Later action
Global Accessibility Awareness Day
Created a nonprofit foundation to extend GAAD’s digital-accessibility mission from awareness into sustained technology-industry action.
Evergreen date guide
What is celebrated on May 20?
See the observances and verified observance-history milestones attached to May 20. Each observance keeps its own source and date details.
Verified history
Today in history →On this date in observance history
Selected observance milestones connected to this date, based on reviewed sources.
2018
First observance
National Rescue Dog Day
The creator site establishes 2018 founding and May 20 recurrence; National Day Calendar says annual observance began in 2018.
2009
Institutional decision
School Bus Driver Appreciation Day
The California Secretary of State 2009 chaptered-resolution table lists Resolution Chapter 32, ACR 58, with Date Filed 05/20/2009.
1998
Institutional decision
Day of the National Flag
The official legislative portal dates Law No. 96/1998 to May 20, 1998.
1972
Precursor
National Day of Cameroon
The referendum anniversary became the historical basis for the recurring May 20 National Day.
1933
Institutional decision
National Maritime Day
The original congressional resolution is dated May 20, 1933.
Curated global anchors
See the collection →Major global guides on May 20
A reviewed starting point drawn from prominent global observances with strong institutional or organizer sources. Each observance keeps its own documented status and scope.
Source-backedFixed AnnualIn-depth guide
World Metrology Day
UNESCO international day
Reviewed depth
Other in-depth guides on May 20
Source-backedFixed AnnualIn-depth guide
Clinical Trials Day
The Association of Clinical Research Professionals states Clinical Trials Day is observed annually on 20 May and documents its 2026 recognition initiative.
Source-backedFixed AnnualIn-depth guide
Independence Restoration Day
Timor-Leste government material identifies 20 May as Independence Restoration Day and as a national holiday under the country’s public-holiday framework.
Source-backedFixed AnnualIn-depth guide
National Day of Cameroon
Cameroon Presidency material identifies May 20 as National Day and links it to the 1972 referendum establishing the Unitary State; ministry sources list May 20 in the legal-holiday framewor…
Source-backedFixed AnnualIn-depth guide
National Rescue Dog Day
The official National Rescue Dog Day site and Tails That Teach identify Lisa Wiehebrink as founder, state the observance was founded in 2018 and maintain annual May 20 recurrence; National…
Source-backedFixed AnnualIn-depth guide
National Women in Aerospace Day
H. Res. 941 was introduced to recognize May 20 as National Women in Aerospace Day, and the Congressional Record documents a May 20, 2026 House recognition statement.
Source-backedFixed AnnualIn-depth guide
Restoration of Independence Day
Timor-Leste Law No. 10/2005 of 10 August establishes 20 May, Restoration of Independence Day, as a fixed-date national public holiday; current government notices continue that legal status.
Explore the mix
All topics →Topics represented on May 20
9 observances
All observances on this date
Source-backedFixed AnnualIn-depth guide
Clinical Trials Day
The Association of Clinical Research Professionals states Clinical Trials Day is observed annually on 20 May and documents its 2026 recognition initiative.
Source-backedFixed AnnualIn-depth guide
Independence Restoration Day
Timor-Leste government material identifies 20 May as Independence Restoration Day and as a national holiday under the country’s public-holiday framework.
Source-backedFixed AnnualIn-depth guide
National Day of Cameroon
Cameroon Presidency material identifies May 20 as National Day and links it to the 1972 referendum establishing the Unitary State; ministry sources list May 20 in the legal-holiday framewor…
Source-backedFixed AnnualIn-depth guide
National Rescue Dog Day
The official National Rescue Dog Day site and Tails That Teach identify Lisa Wiehebrink as founder, state the observance was founded in 2018 and maintain annual May 20 recurrence; National…
Source-backedFixed AnnualIn-depth guide
National Women in Aerospace Day
H. Res. 941 was introduced to recognize May 20 as National Women in Aerospace Day, and the Congressional Record documents a May 20, 2026 House recognition statement.
Source-backedFixed AnnualIn-depth guide
Restoration of Independence Day
Timor-Leste Law No. 10/2005 of 10 August establishes 20 May, Restoration of Independence Day, as a fixed-date national public holiday; current government notices continue that legal status.
Source-backedFixed AnnualIn-depth guide
World AUTOimmune & AUTOinflammatory Arthritis Day
AiArthritis identifies May 20 as World AUTOimmune & AUTOinflammatory Arthritis Day, says the International Foundation established the awareness day in 2012, and identifies itself as the off…
Source-backedFixed AnnualIn-depth guide
World Bee Day
A/RES/72/211
Source-backedFixed AnnualIn-depth guide
World Metrology Day
UNESCO international day
How dates are selected
This page combines fixed annual dates, reusable calendar rules and year-specific dates confirmed for 2026. Variable or historical dates are included only when they are clearly supported.
Read the methodology →